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diff --git a/pod/perllocale.pod b/pod/perllocale.pod new file mode 100644 index 0000000000..e1bf5f070d --- /dev/null +++ b/pod/perllocale.pod @@ -0,0 +1,800 @@ +=head1 NAME + +perllocale - Perl locale handling (internationalization and localization) + +=head1 DESCRIPTION + +Perl supports language-specific notions of data such as "is this a +letter", "what is the uppercase equivalent of this letter", and "which +of these letters comes first". These are important issues, especially +for languages other than English - but also for English: it would be +very naE<iuml>ve to think that C<A-Za-z> defines all the "letters". Perl +is also aware that some character other than '.' may be preferred as a +decimal point, and that output date representations may be +language-specific. The process of making an application take account of +its users' preferences in such matters is called B<internationalization> +(often abbreviated as B<i18n>); telling such an application about a +particular set of preferences is known as B<localization> (B<l10n>). + +Perl can understand language-specific data via the standardized (ISO C, +XPG4, POSIX 1.c) method called "the locale system". The locale system is +controlled per application using one pragma, one function call, and +several environment variables. + +B<NOTE>: This feature is new in Perl 5.004, and does not apply unless an +application specifically requests it - see L<Backward compatibility>. +The one exception is that write() now B<always> uses the current locale +- see L<"NOTES">. + +=head1 PREPARING TO USE LOCALES + +If Perl applications are to be able to understand and present your data +correctly according a locale of your choice, B<all> of the following +must be true: + +=over 4 + +=item * + +B<Your operating system must support the locale system>. If it does, +you should find that the setlocale() function is a documented part of +its C library. + +=item * + +B<Definitions for the locales which you use must be installed>. You, or +your system administrator, must make sure that this is the case. The +available locales, the location in which they are kept, and the manner +in which they are installed, vary from system to system. Some systems +provide only a few, hard-wired, locales, and do not allow more to be +added; others allow you to add "canned" locales provided by the system +supplier; still others allow you or the system administrator to define +and add arbitrary locales. (You may have to ask your supplier to +provide canned locales which are not delivered with your operating +system.) Read your system documentation for further illumination. + +=item * + +B<Perl must believe that the locale system is supported>. If it does, +C<perl -V:d_setlocale> will say that the value for C<d_setlocale> is +C<define>. + +=back + +If you want a Perl application to process and present your data +according to a particular locale, the application code should include +the S<C<use locale>> pragma (see L<The use locale pragma>) where +appropriate, and B<at least one> of the following must be true: + +=over 4 + +=item * + +B<The locale-determining environment variables (see L<"ENVIRONMENT">) +must be correctly set up>, either by yourself, or by the person who set +up your system account, at the time the application is started. + +=item * + +B<The application must set its own locale> using the method described in +L<The setlocale function>. + +=back + +=head1 USING LOCALES + +=head2 The use locale pragma + +By default, Perl ignores the current locale. The S<C<use locale>> +pragma tells Perl to use the current locale for some operations: + +=over 4 + +=item * + +B<The comparison operators> (C<lt>, C<le>, C<cmp>, C<ge>, and C<gt>) and +the POSIX string collation functions strcoll() and strxfrm() use +C<LC_COLLATE>. sort() is also affected if it is used without an +explicit comparison function because it uses C<cmp> by default. + +B<Note:> C<eq> and C<ne> are unaffected by the locale: they always +perform a byte-by-byte comparison of their scalar operands. What's +more, if C<cmp> finds that its operands are equal according to the +collation sequence specified by the current locale, it goes on to +perform a byte-by-byte comparison, and only returns I<0> (equal) if the +operands are bit-for-bit identical. If you really want to know whether +two strings - which C<eq> and C<cmp> may consider different - are equal +as far as collation in the locale is concerned, see the discussion in +L<Category LC_COLLATE: Collation>. + +=item * + +B<Regular expressions and case-modification functions> (uc(), lc(), +ucfirst(), and lcfirst()) use C<LC_CTYPE> + +=item * + +B<The formatting functions> (printf(), sprintf() and write()) use +C<LC_NUMERIC> + +=item * + +B<The POSIX date formatting function> (strftime()) uses C<LC_TIME>. + +=back + +C<LC_COLLATE>, C<LC_CTYPE>, and so on, are discussed further in L<LOCALE +CATEGORIES>. + +The default behavior returns with S<C<no locale>> or on reaching the +end of the enclosing block. + +Note that the string result of any operation that uses locale +information is tainted, as it is possible for a locale to be +untrustworthy. See L<"SECURITY">. + +=head2 The setlocale function + +You can switch locales as often as you wish at run time with the +POSIX::setlocale() function: + + # This functionality not usable prior to Perl 5.004 + require 5.004; + + # Import locale-handling tool set from POSIX module. + # This example uses: setlocale -- the function call + # LC_CTYPE -- explained below + use POSIX qw(locale_h); + + # query and save the old locale + $old_locale = setlocale(LC_CTYPE); + + setlocale(LC_CTYPE, "fr_CA.ISO8859-1"); + # LC_CTYPE now in locale "French, Canada, codeset ISO 8859-1" + + setlocale(LC_CTYPE, ""); + # LC_CTYPE now reset to default defined by LC_ALL/LC_CTYPE/LANG + # environment variables. See below for documentation. + + # restore the old locale + setlocale(LC_CTYPE, $old_locale); + +The first argument of setlocale() gives the B<category>, the second the +B<locale>. The category tells in what aspect of data processing you +want to apply locale-specific rules. Category names are discussed in +L<LOCALE CATEGORIES> and L<"ENVIRONMENT">. The locale is the name of a +collection of customization information corresponding to a particular +combination of language, country or territory, and codeset. Read on for +hints on the naming of locales: not all systems name locales as in the +example. + +If no second argument is provided, the function returns a string naming +the current locale for the category. You can use this value as the +second argument in a subsequent call to setlocale(). If a second +argument is given and it corresponds to a valid locale, the locale for +the category is set to that value, and the function returns the +now-current locale value. You can use this in a subsequent call to +setlocale(). (In some implementations, the return value may sometimes +differ from the value you gave as the second argument - think of it as +an alias for the value that you gave.) + +As the example shows, if the second argument is an empty string, the +category's locale is returned to the default specified by the +corresponding environment variables. Generally, this results in a +return to the default which was in force when Perl started up: changes +to the environment made by the application after startup may or may not +be noticed, depending on the implementation of your system's C library. + +If the second argument does not correspond to a valid locale, the locale +for the category is not changed, and the function returns I<undef>. + +For further information about the categories, consult L<setlocale(3)>. +For the locales available in your system, also consult L<setlocale(3)> +and see whether it leads you to the list of the available locales +(search for the I<SEE ALSO> section). If that fails, try the following +command lines: + + locale -a + + nlsinfo + + ls /usr/lib/nls/loc + + ls /usr/lib/locale + + ls /usr/lib/nls + +and see whether they list something resembling these + + en_US.ISO8859-1 de_DE.ISO8859-1 ru_RU.ISO8859-5 + en_US de_DE ru_RU + en de ru + english german russian + english.iso88591 german.iso88591 russian.iso88595 + +Sadly, even though the calling interface for setlocale() has been +standardized, the names of the locales and the directories where +the configuration is, have not. The basic form of the name is +I<language_country/territory>B<.>I<codeset>, but the +latter parts are not always present. + +Two special locales are worth particular mention: "C" and "POSIX". +Currently these are effectively the same locale: the difference is +mainly that the first one is defined by the C standard and the second by +the POSIX standard. What they define is the B<default locale> in which +every program starts in the absence of locale information in its +environment. (The default default locale, if you will.) Its language +is (American) English and its character codeset ASCII. + +B<NOTE>: Not all systems have the "POSIX" locale (not all systems are +POSIX-conformant), so use "C" when you need explicitly to specify this +default locale. + +=head2 The localeconv function + +The POSIX::localeconv() function allows you to get particulars of the +locale-dependent numeric formatting information specified by the current +C<LC_NUMERIC> and C<LC_MONETARY> locales. (If you just want the name of +the current locale for a particular category, use POSIX::setlocale() +with a single parameter - see L<The setlocale function>.) + + use POSIX qw(locale_h); + + # Get a reference to a hash of locale-dependent info + $locale_values = localeconv(); + + # Output sorted list of the values + for (sort keys %$locale_values) { + printf "%-20s = %s\n", $_, $locale_values->{$_} + } + +localeconv() takes no arguments, and returns B<a reference to> a hash. +The keys of this hash are formatting variable names such as +C<decimal_point> and C<thousands_sep>; the values are the corresponding +values. See L<POSIX (3)/localeconv> for a longer example, which lists +all the categories an implementation might be expected to provide; some +provide more and others fewer, however. Note that you don't need C<use +locale>: as a function with the job of querying the locale, localeconv() +always observes the current locale. + +Here's a simple-minded example program which rewrites its command line +parameters as integers formatted correctly in the current locale: + + # See comments in previous example + require 5.004; + use POSIX qw(locale_h); + + # Get some of locale's numeric formatting parameters + my ($thousands_sep, $grouping) = + @{localeconv()}{'thousands_sep', 'grouping'}; + + # Apply defaults if values are missing + $thousands_sep = ',' unless $thousands_sep; + $grouping = 3 unless $grouping; + + # Format command line params for current locale + for (@ARGV) { + $_ = int; # Chop non-integer part + 1 while + s/(\d)(\d{$grouping}($|$thousands_sep))/$1$thousands_sep$2/; + print "$_"; + } + print "\n"; + +=head1 LOCALE CATEGORIES + +The subsections which follow describe basic locale categories. As well +as these, there are some combination categories which allow the +manipulation of more than one basic category at a time. See +L<"ENVIRONMENT"> for a discussion of these. + +=head2 Category LC_COLLATE: Collation + +When in the scope of S<C<use locale>>, Perl looks to the C<LC_COLLATE> +environment variable to determine the application's notions on the +collation (ordering) of characters. ('b' follows 'a' in Latin +alphabets, but where do 'E<aacute>' and 'E<aring>' belong?) + +Here is a code snippet that will tell you what are the alphanumeric +characters in the current locale, in the locale order: + + use locale; + print +(sort grep /\w/, map { chr() } 0..255), "\n"; + +Compare this with the characters that you see and their order if you +state explicitly that the locale should be ignored: + + no locale; + print +(sort grep /\w/, map { chr() } 0..255), "\n"; + +This machine-native collation (which is what you get unless S<C<use +locale>> has appeared earlier in the same block) must be used for +sorting raw binary data, whereas the locale-dependent collation of the +first example is useful for natural text. + +As noted in L<USING LOCALES>, C<cmp> compares according to the current +collation locale when C<use locale> is in effect, but falls back to a +byte-by-byte comparison for strings which the locale says are equal. You +can use POSIX::strcoll() if you don't want this fall-back: + + use POSIX qw(strcoll); + $equal_in_locale = + !strcoll("space and case ignored", "SpaceAndCaseIgnored"); + +$equal_in_locale will be true if the collation locale specifies a +dictionary-like ordering which ignores space characters completely, and +which folds case. + +If you have a single string which you want to check for "equality in +locale" against several others, you might think you could gain a little +efficiency by using POSIX::strxfrm() in conjunction with C<eq>: + + use POSIX qw(strxfrm); + $xfrm_string = strxfrm("Mixed-case string"); + print "locale collation ignores spaces\n" + if $xfrm_string eq strxfrm("Mixed-casestring"); + print "locale collation ignores hyphens\n" + if $xfrm_string eq strxfrm("Mixedcase string"); + print "locale collation ignores case\n" + if $xfrm_string eq strxfrm("mixed-case string"); + +strxfrm() takes a string and maps it into a transformed string for use +in byte-by-byte comparisons against other transformed strings during +collation. "Under the hood", locale-affected Perl comparison operators +call strxfrm() for both their operands, then do a byte-by-byte +comparison of the transformed strings. By calling strxfrm() explicitly, +and using a non locale-affected comparison, the example attempts to save +a couple of transformations. In fact, it doesn't save anything: Perl +magic (see L<perlguts/Magic Variables>) creates the transformed version of a +string the first time it's needed in a comparison, then keeps it around +in case it's needed again. An example rewritten the easy way with +C<cmp> runs just about as fast. It also copes with null characters +embedded in strings; if you call strxfrm() directly, it treats the first +null it finds as a terminator. And don't expect the transformed strings +it produces to be portable across systems - or even from one revision +of your operating system to the next. In short, don't call strxfrm() +directly: let Perl do it for you. + +Note: C<use locale> isn't shown in some of these examples, as it isn't +needed: strcoll() and strxfrm() exist only to generate locale-dependent +results, and so always obey the current C<LC_COLLATE> locale. + +=head2 Category LC_CTYPE: Character Types + +When in the scope of S<C<use locale>>, Perl obeys the C<LC_CTYPE> locale +setting. This controls the application's notion of which characters are +alphabetic. This affects Perl's C<\w> regular expression metanotation, +which stands for alphanumeric characters - that is, alphabetic and +numeric characters. (Consult L<perlre> for more information about +regular expressions.) Thanks to C<LC_CTYPE>, depending on your locale +setting, characters like 'E<aelig>', 'E<eth>', 'E<szlig>', and +'E<oslash>' may be understood as C<\w> characters. + +The C<LC_CTYPE> locale also provides the map used in translating +characters between lower and uppercase. This affects the case-mapping +functions - lc(), lcfirst, uc() and ucfirst(); case-mapping +interpolation with C<\l>, C<\L>, C<\u> or <\U> in double-quoted strings +and in C<s///> substitutions; and case-independent regular expression +pattern matching using the C<i> modifier. + +Finally, C<LC_CTYPE> affects the POSIX character-class test functions - +isalpha(), islower() and so on. For example, if you move from the "C" +locale to a 7-bit Scandinavian one, you may find - possibly to your +surprise - that "|" moves from the ispunct() class to isalpha(). + +B<Note:> A broken or malicious C<LC_CTYPE> locale definition may result +in clearly ineligible characters being considered to be alphanumeric by +your application. For strict matching of (unaccented) letters and +digits - for example, in command strings - locale-aware applications +should use C<\w> inside a C<no locale> block. See L<"SECURITY">. + +=head2 Category LC_NUMERIC: Numeric Formatting + +When in the scope of S<C<use locale>>, Perl obeys the C<LC_NUMERIC> +locale information, which controls application's idea of how numbers +should be formatted for human readability by the printf(), sprintf(), +and write() functions. String to numeric conversion by the +POSIX::strtod() function is also affected. In most implementations the +only effect is to change the character used for the decimal point - +perhaps from '.' to ',': these functions aren't aware of such niceties +as thousands separation and so on. (See L<The localeconv function> if +you care about these things.) + +Note that output produced by print() is B<never> affected by the +current locale: it is independent of whether C<use locale> or C<no +locale> is in effect, and corresponds to what you'd get from printf() +in the "C" locale. The same is true for Perl's internal conversions +between numeric and string formats: + + use POSIX qw(strtod); + use locale; + + $n = 5/2; # Assign numeric 2.5 to $n + + $a = " $n"; # Locale-independent conversion to string + + print "half five is $n\n"; # Locale-independent output + + printf "half five is %g\n", $n; # Locale-dependent output + + print "DECIMAL POINT IS COMMA\n" + if $n == (strtod("2,5"))[0]; # Locale-dependent conversion + +=head2 Category LC_MONETARY: Formatting of monetary amounts + +The C standard defines the C<LC_MONETARY> category, but no function that +is affected by its contents. (Those with experience of standards +committees will recognize that the working group decided to punt on the +issue.) Consequently, Perl takes no notice of it. If you really want +to use C<LC_MONETARY>, you can query its contents - see L<The localeconv +function> - and use the information that it returns in your +application's own formatting of currency amounts. However, you may well +find that the information, though voluminous and complex, does not quite +meet your requirements: currency formatting is a hard nut to crack. + +=head2 LC_TIME + +The output produced by POSIX::strftime(), which builds a formatted +human-readable date/time string, is affected by the current C<LC_TIME> +locale. Thus, in a French locale, the output produced by the C<%B> +format element (full month name) for the first month of the year would +be "janvier". Here's how to get a list of the long month names in the +current locale: + + use POSIX qw(strftime); + for (0..11) { + $long_month_name[$_] = + strftime("%B", 0, 0, 0, 1, $_, 96); + } + +Note: C<use locale> isn't needed in this example: as a function which +exists only to generate locale-dependent results, strftime() always +obeys the current C<LC_TIME> locale. + +=head2 Other categories + +The remaining locale category, C<LC_MESSAGES> (possibly supplemented by +others in particular implementations) is not currently used by Perl - +except possibly to affect the behavior of library functions called by +extensions which are not part of the standard Perl distribution. + +=head1 SECURITY + +While the main discussion of Perl security issues can be found in +L<perlsec>, a discussion of Perl's locale handling would be incomplete +if it did not draw your attention to locale-dependent security issues. +Locales - particularly on systems which allow unprivileged users to +build their own locales - are untrustworthy. A malicious (or just plain +broken) locale can make a locale-aware application give unexpected +results. Here are a few possibilities: + +=over 4 + +=item * + +Regular expression checks for safe file names or mail addresses using +C<\w> may be spoofed by an C<LC_CTYPE> locale which claims that +characters such as "E<gt>" and "|" are alphanumeric. + +=item * + +String interpolation with case-mapping, as in, say, C<$dest = +"C:\U$name.$ext">, may produce dangerous results if a bogus LC_CTYPE +case-mapping table is in effect. + +=item * + +If the decimal point character in the C<LC_NUMERIC> locale is +surreptitiously changed from a dot to a comma, C<sprintf("%g", +0.123456e3)> produces a string result of "123,456". Many people would +interpret this as one hundred and twenty-three thousand, four hundred +and fifty-six. + +=item * + +A sneaky C<LC_COLLATE> locale could result in the names of students with +"D" grades appearing ahead of those with "A"s. + +=item * + +An application which takes the trouble to use the information in +C<LC_MONETARY> may format debits as if they were credits and vice versa +if that locale has been subverted. Or it make may make payments in US +dollars instead of Hong Kong dollars. + +=item * + +The date and day names in dates formatted by strftime() could be +manipulated to advantage by a malicious user able to subvert the +C<LC_DATE> locale. ("Look - it says I wasn't in the building on +Sunday.") + +=back + +Such dangers are not peculiar to the locale system: any aspect of an +application's environment which may maliciously be modified presents +similar challenges. Similarly, they are not specific to Perl: any +programming language which allows you to write programs which take +account of their environment exposes you to these issues. + +Perl cannot protect you from all of the possibilities shown in the +examples - there is no substitute for your own vigilance - but, when +C<use locale> is in effect, Perl uses the tainting mechanism (see +L<perlsec>) to mark string results which become locale-dependent, and +which may be untrustworthy in consequence. Here is a summary of the +tainting behavior of operators and functions which may be affected by +the locale: + +=over 4 + +=item B<Comparison operators> (C<lt>, C<le>, C<ge>, C<gt> and C<cmp>): + +Scalar true/false (or less/equal/greater) result is never tainted. + +=item B<Case-mapping interpolation> (with C<\l>, C<\L>, C<\u> or <\U>) + +Result string containing interpolated material is tainted if +C<use locale> is in effect. + +=item B<Matching operator> (C<m//>): + +Scalar true/false result never tainted. + +Subpatterns, either delivered as an array-context result, or as $1 etc. +are tainted if C<use locale> is in effect, and the subpattern regular +expression contains C<\w> (to match an alphanumeric character), C<\W> +(non-alphanumeric character), C<\s> (white-space character), or C<\S> +(non white-space character). The matched pattern variable, $&, $` +(pre-match), $' (post-match), and $+ (last match) are also tainted if +C<use locale> is in effect and the regular expression contains C<\w>, +C<\W>, C<\s>, or C<\S>. + +=item B<Substitution operator> (C<s///>): + +Has the same behavior as the match operator. Also, the left +operand of C<=~> becomes tainted when C<use locale> in effect, +if it is modified as a result of a substitution based on a regular +expression match involving C<\w>, C<\W>, C<\s>, or C<\S>; or of +case-mapping with C<\l>, C<\L>,C<\u> or <\U>. + +=item B<In-memory formatting function> (sprintf()): + +Result is tainted if "use locale" is in effect. + +=item B<Output formatting functions> (printf() and write()): + +Success/failure result is never tainted. + +=item B<Case-mapping functions> (lc(), lcfirst(), uc(), ucfirst()): + +Results are tainted if C<use locale> is in effect. + +=item B<POSIX locale-dependent functions> (localeconv(), strcoll(), +strftime(), strxfrm()): + +Results are never tainted. + +=item B<POSIX character class tests> (isalnum(), isalpha(), isdigit(), +isgraph(), islower(), isprint(), ispunct(), isspace(), isupper(), +isxdigit()): + +True/false results are never tainted. + +=back + +Three examples illustrate locale-dependent tainting. +The first program, which ignores its locale, won't run: a value taken +directly from the command line may not be used to name an output file +when taint checks are enabled. + + #/usr/local/bin/perl -T + # Run with taint checking + + # Command line sanity check omitted... + $tainted_output_file = shift; + + open(F, ">$tainted_output_file") + or warn "Open of $untainted_output_file failed: $!\n"; + +The program can be made to run by "laundering" the tainted value through +a regular expression: the second example - which still ignores locale +information - runs, creating the file named on its command line +if it can. + + #/usr/local/bin/perl -T + + $tainted_output_file = shift; + $tainted_output_file =~ m%[\w/]+%; + $untainted_output_file = $&; + + open(F, ">$untainted_output_file") + or warn "Open of $untainted_output_file failed: $!\n"; + +Compare this with a very similar program which is locale-aware: + + #/usr/local/bin/perl -T + + $tainted_output_file = shift; + use locale; + $tainted_output_file =~ m%[\w/]+%; + $localized_output_file = $&; + + open(F, ">$localized_output_file") + or warn "Open of $localized_output_file failed: $!\n"; + +This third program fails to run because $& is tainted: it is the result +of a match involving C<\w> when C<use locale> is in effect. + +=head1 ENVIRONMENT + +=over 12 + +=item PERL_BADLANG + +A string that can suppress Perl's warning about failed locale settings +at startup. Failure can occur if the locale support in the operating +system is lacking (broken) is some way - or if you mistyped the name of +a locale when you set up your environment. If this environment variable +is absent, or has a value which does not evaluate to integer zero - that +is "0" or "" - Perl will complain about locale setting failures. + +B<NOTE>: PERL_BADLANG only gives you a way to hide the warning message. +The message tells about some problem in your system's locale support, +and you should investigate what the problem is. + +=back + +The following environment variables are not specific to Perl: They are +part of the standardized (ISO C, XPG4, POSIX 1.c) setlocale() method +for controlling an application's opinion on data. + +=over 12 + +=item LC_ALL + +C<LC_ALL> is the "override-all" locale environment variable. If it is +set, it overrides all the rest of the locale environment variables. + +=item LC_CTYPE + +In the absence of C<LC_ALL>, C<LC_CTYPE> chooses the character type +locale. In the absence of both C<LC_ALL> and C<LC_CTYPE>, C<LANG> +chooses the character type locale. + +=item LC_COLLATE + +In the absence of C<LC_ALL>, C<LC_COLLATE> chooses the collation +(sorting) locale. In the absence of both C<LC_ALL> and C<LC_COLLATE>, +C<LANG> chooses the collation locale. + +=item LC_MONETARY + +In the absence of C<LC_ALL>, C<LC_MONETARY> chooses the monetary +formatting locale. In the absence of both C<LC_ALL> and C<LC_MONETARY>, +C<LANG> chooses the monetary formatting locale. + +=item LC_NUMERIC + +In the absence of C<LC_ALL>, C<LC_NUMERIC> chooses the numeric format +locale. In the absence of both C<LC_ALL> and C<LC_NUMERIC>, C<LANG> +chooses the numeric format. + +=item LC_TIME + +In the absence of C<LC_ALL>, C<LC_TIME> chooses the date and time +formatting locale. In the absence of both C<LC_ALL> and C<LC_TIME>, +C<LANG> chooses the date and time formatting locale. + +=item LANG + +C<LANG> is the "catch-all" locale environment variable. If it is set, it +is used as the last resort after the overall C<LC_ALL> and the +category-specific C<LC_...>. + +=back + +=head1 NOTES + +=head2 Backward compatibility + +Versions of Perl prior to 5.004 B<mostly> ignored locale information, +generally behaving as if something similar to the C<"C"> locale (see +L<The setlocale function>) was always in force, even if the program +environment suggested otherwise. By default, Perl still behaves this +way so as to maintain backward compatibility. If you want a Perl +application to pay attention to locale information, you B<must> use +the S<C<use locale>> pragma (see L<The use locale Pragma>) to +instruct it to do so. + +Versions of Perl from 5.002 to 5.003 did use the C<LC_CTYPE> +information if that was available, that is, C<\w> did understand what +are the letters according to the locale environment variables. +The problem was that the user had no control over the feature: +if the C library supported locales, Perl used them. + +=head2 I18N:Collate obsolete + +In versions of Perl prior to 5.004 per-locale collation was possible +using the C<I18N::Collate> library module. This module is now mildly +obsolete and should be avoided in new applications. The C<LC_COLLATE> +functionality is now integrated into the Perl core language: One can +use locale-specific scalar data completely normally with C<use locale>, +so there is no longer any need to juggle with the scalar references of +C<I18N::Collate>. + +=head2 Sort speed and memory use impacts + +Comparing and sorting by locale is usually slower than the default +sorting; slow-downs of two to four times have been observed. It will +also consume more memory: once a Perl scalar variable has participated +in any string comparison or sorting operation obeying the locale +collation rules, it will take 3-15 times more memory than before. (The +exact multiplier depends on the string's contents, the operating system +and the locale.) These downsides are dictated more by the operating +system's implementation of the locale system than by Perl. + +=head2 write() and LC_NUMERIC + +Formats are the only part of Perl which unconditionally use information +from a program's locale; if a program's environment specifies an +LC_NUMERIC locale, it is always used to specify the decimal point +character in formatted output. Formatted output cannot be controlled by +C<use locale> because the pragma is tied to the block structure of the +program, and, for historical reasons, formats exist outside that block +structure. + +=head2 Freely available locale definitions + +There is a large collection of locale definitions at +C<ftp://dkuug.dk/i18n/WG15-collection>. You should be aware that it is +unsupported, and is not claimed to be fit for any purpose. If your +system allows the installation of arbitrary locales, you may find the +definitions useful as they are, or as a basis for the development of +your own locales. + +=head2 I18n and l10n + +"Internationalization" is often abbreviated as B<i18n> because its first +and last letters are separated by eighteen others. (You may guess why +the internalin ... internaliti ... i18n tends to get abbreviated.) In +the same way, "localization" is often abbreviated to B<l10n>. + +=head2 An imperfect standard + +Internationalization, as defined in the C and POSIX standards, can be +criticized as incomplete, ungainly, and having too large a granularity. +(Locales apply to a whole process, when it would arguably be more useful +to have them apply to a single thread, window group, or whatever.) They +also have a tendency, like standards groups, to divide the world into +nations, when we all know that the world can equally well be divided +into bankers, bikers, gamers, and so on. But, for now, it's the only +standard we've got. This may be construed as a bug. + +=head1 BUGS + +=head2 Broken systems + +In certain system environments the operating system's locale support +is broken and cannot be fixed or used by Perl. Such deficiencies can +and will result in mysterious hangs and/or Perl core dumps when the +C<use locale> is in effect. When confronted with such a system, +please report in excruciating detail to <F<perlbug@perl.com>>, and +complain to your vendor: maybe some bug fixes exist for these problems +in your operating system. Sometimes such bug fixes are called an +operating system upgrade. + +=head1 SEE ALSO + +L<POSIX (3)/isalnum>, L<POSIX (3)/isalpha>, L<POSIX (3)/isdigit>, +L<POSIX (3)/isgraph>, L<POSIX (3)/islower>, L<POSIX (3)/isprint>, +L<POSIX (3)/ispunct>, L<POSIX (3)/isspace>, L<POSIX (3)/isupper>, +L<POSIX (3)/isxdigit>, L<POSIX (3)/localeconv>, L<POSIX (3)/setlocale>, +L<POSIX (3)/strcoll>, L<POSIX (3)/strftime>, L<POSIX (3)/strtod>, +L<POSIX (3)/strxfrm> + +=head1 HISTORY + +Jarkko Hietaniemi's original F<perli18n.pod> heavily hacked by Dominic +Dunlop, assisted by the perl5-porters. + +Last update: Wed Jan 22 11:04:58 EST 1997 |